When large amounts of radiation are released into the air over a short period of time (as from a nuclear blast), the health consequences can be serious. Radiation sickness can cause flu-like symptoms, hair loss, skin burns, and even death.

Fortunately, radiation sickness is rare and the risk to people more than a few miles from a blast is extremely low.

If radiation remains in the soil or water supplies, long-term exposure can increase a person's risk of cancer. But even then, it's much lower than the overall risk of cancer to most people living in the United States today.

Here's more about radiation and what happens when people are exposed to high amounts of it.

About Radiation

Radiation is tricky to understand because you can't see it. In the broadest sense, it's the release of energy. This energy can travel in the form or particles or rays. So, for example, the sun is one energy source that gives off (or "radiates") energy through particles and rays.

In just the right amounts, radiation is a good thing. It's necessary for life and is found just about everywhere: in the earth's soil, the water we drink, the food we eat, in building materials, even our bodies.

Non-ionizing radiation is on the low end of the electromagnetic spectrum (referred to as "low-frequency"). While still harmful in very high doses, this type of radiation cannot change the molecular chemistry of a person or thing.

Ionizing radiation. Some natural sources of ionizing radiation are cosmic rays from the sun and stars, and radon (an element found in soil). Manmade sources include X-ray and CT machines, and radiation therapy for cancer treatment.

This type of radiation is considered high-frequency and can be powerful enough to split an atom and change the molecular chemistry of a person or thing. In people, high doses of ionizing radiation can alter DNA, which can be useful (in the case of cancer therapy), but also harmful in unregulated doses — and this can lead to radiation sickness and even death.

How Much Radiation Exposure Is Considered Safe?

Every day, all around us, we're being exposed to radiation. The government ensures that the levels of radiation we're exposed to are well within safety limits by setting restrictions through the U.S. Nuclear Regulatory Commission (NRC).

Radiation is measured in units called "sieverts." The NRC estimates that, on average, Americans are exposed to 3.2 millisieverts (mSv) per year in daily life. This is called "background radiation" and is considered a safe amount of radiation exposure.

It's possible, however, to be exposed to more radiation and still be within safety limits. The NRC sets 10 mSv as the annual safety limit for radiation exposure that's unrelated to medical tests or treatments. That number can be higher for people who need to be exposed to radiation for medical reasons, but it's the responsibility of radiologists and other nuclear medicine practitioners to make sure the amount of radiation people receive is as low as possible.

Can I Be Exposed to Too Much Radiation?

It's rare to be exposed to dangerously high doses of radiation in everyday life. Someone could be exposed to high doses, however, in the event of a nuclear blast (as in Hiroshima and Nagasaki in World War II) or a nuclear power plant failure (which happened in the Sendai region of Japan after a tsunami in 2011).

With events like these, people who are in the immediate vicinity — within a few miles of the explosion or other radiation-releasing event — are at risk of being exposed to increased levels of ionizing radiation.

But unless someone is standing inside a nuclear reactor building when the explosion takes place, the chances of developing radiation sickness or sudden death are low. That's because the farther away from the source of radiation a person is, the lower the risk. In fact, radiation dissipates very quickly, so while someone who is 20 feet away from an explosion can suffer life-threatening complications, someone who is just 40 feet away absorbs one quarter of the dose, and a lower risk of radiation sickness.

Effects of Radiation Sickness

Radiation sickness is extremely rare, and usually only happens in people who have been exposed to 300 or more times the average yearly dose of background radiation (3.2 mSv). This is usually only possible through a nuclear disaster.

In the event of such a disaster, someone exposed to high doses of radiation might experience these symptoms:

a drop in blood cell counts

hair loss

nausea

vomiting

diarrhea

skin burns

an eventual increased risk in blood and thyroid cancers

eventual death as a result of organ failure

The severity of these symptoms and when they develop in the body varies depending on how much radiation a person was exposed to, and the duration of the exposure. When exposure is sudden and upwards of 100 or more times the average yearly dose, symptoms can be severe and appear within a few hours. A lower dose of radiation over a longer period of time is less likely to cause symptoms right away, but will still increase the risk of cancer later in life.

Many people who believe they've been exposed to radiation in any amount worry about their eventual risk of cancer. Studies on the nuclear attacks on Japan during World War II found that the bombing victims were at an increased risk for cancer after the attack. Unborn babies and young children were most susceptible, because their tissues were still growing and developing.

The increased risk of cancer for people exposed to radiation is still significantly lower than the overall risk of developing cancer in the United States today, which the American Cancer Society reports as 40% (meaning that 2 in 5 Americans will develop cancer in their lifetimes).

Treatment

Most people who are exposed to near-lethal amounts of radiation and survive usually face lifelong health problems as a result of the exposure. Medical care involves a multidisciplinary approach to help treat areas of the body that were damaged by the radiation, including the immune system and blood supply.

In cases where medical personnel can identify and begin treating people exposed to radiation soon after an event, prescription medication (potassium iodide) may be administered to help lower the risk of thyroid cancer. But this medication can only be given within a 24-hour period to be effective — taking it later on can cause serious complications to the thyroid gland. This medication can also be used preventatively prior to exposure.

Effects on the Environment and Food Supply

After the initial shock of a nuclear disaster and the immediate health concerns, people start to question the effects that radiation has on the environment, water, and food. Unfortunately, there's no way to know how much damage has been done until months or even years later.

After a nuclear blast, radiation particles can travel on wind currents for miles and settle in water sources, plants, and soil. Livestock and food crops in these areas are likely to be affected, causing food supplies to become contaminated.

Sometimes the level of radiation in food is so minute it poses no risk, but other times it rises above safety levels. So scientists test the levels of radiation in the soil after a nuclear disaster to determine the risks. Food that's deemed unsafe is banned until radiation levels decrease — a process that can take weeks, months, or years depending on the amount and type of radiation.

While people can avoid eating contaminated food, wild animals in affected areas cannot. Fortunately, though, studies from previous nuclear disasters have found that while some animals might incur short-term harm from radiation exposure, most do not suffer long-term health problems.